Games : Buy Imperial Edition or wait for ESO Unlimited and what DLCs exist?

I'm debating right now on this final day of whether to purchase the ESO Imperial Edition or just wait for the Unlimited Edition to be released tomorrow. In our case we're going to get four copies for our family to play together.

I see that the Premium subscription comes with access to:

• a new in-game digital currency store,


• all DLCs


• and a 10% bonus to:
  
  
  
  • XP
  
  
  • gold gain
  
  
  • crafting research
  
  
  • inspiration
  
  
  
  

What does it mean "all DLCs?" What DLCs are there to date and does anyone know if there would be a flat rate purchase option for future DLCs?

By purchasing the Imperial Edition it seems one would get all DLCs to date as well as the potential XP bonus via the Rings of Mara.

Any clarification and understanding of the pros and cons here would be much appreciated.